ECOLOGY AND TAXONOMY OF Holimeda 



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Fig. 102b. The lagoon floor, here near the base of south Medreii pinnacle at approxi- 

 mately — 40 ni, appears to be essentially barren of Halimedae, although the occasional 

 plants were observed. Some of the erect structures in this photograph in the sand 

 near the rock outcrop, height approximately 8 cm, are cylindracea. 



to — 5 m on the lagoon reefs of Jimini. Among green algae Tydemania 

 is second only to Holimeda as a carbonate producer at Enewetak. 



Other noteworthy algal associates of Holimeda on vertical or near 

 vertical faces of pinnacles, particularly below 20 m, were species of 

 Cyanophyta, their reddish or purply filaments at times streaming from 

 under overlapping plates of coral colonies. Masses of some of these 

 filaments also grew out of the sand-rock substrate some distance from 

 pinnacles. 



These Holimeda populations of the sides of pinnacles require more 

 study because they may well be principal suppliers of carbonate to the 

 reef floor. Gilmartin (1960) showed, and our own dives confirm, that the 

 lagoon floors have very low densities of Halimedae growing on them, 

 and yet there are the various bits of drill-core evidence that Holimeda 

 segments are important constituents of the lagoonal sediments 

 (Section IX). Holimeda macrophysa and some of the Opuntioids growing 



